With the advent of use of fiber optical cable as an information transmitting medium, there has been generated a need to install such fiber optical cables in lengths of conduit extending throughout buildings and between buildings. As compared to standard insulated copper or aluminum cable and even telephone wire installed in the past by cable pullers, fiber optical cable requires a more sophisticated puller in terms of having variable speed and having closer control of pull forces generated on the cable to minimize damage to the cable from pulling forces.
A motor speed control circuit for an appliance is disclosed in the Contri U.S. Pat. No. 4,326,153 issued Apr. 20, 1982. The patent provides a circuit for triggering a triac to pass current to the appliance motor when a synchronous ramp or sawtooth reference voltage is less than a speed error voltage, providing accurate timing of the switching point of the triac to control the motor.
The Gisske U.S. Pat. No. 4,568,864 issued Feb. 4, 1986, provides an electric motor control for a pipe or conduit bender wherein a logic system controls an SCR bridge system. The bridge system is supplied from A.C. mains through a bridge rectifier having three diodes and one SCR. For motor drive, this one SCR is made conducting to provide full-rectification, and for motor termination, this SCR is turned off to provide a half-wave rectifier that facilitates turn-off of the motor controlling SCR's.
The Plummer et al U.S. Pat. No. 4,555,093 issued Nov. 26, 1985, illustrates a cable pulling device having an ammeter calibrated to visually display cable pulling force in response to amperage drawn by the motor and a circuit breaker for interrupting power when motor over-load is approached.